Qt: Show a warning when save file can't be opened

CHANGES

@@ -54,6 +54,7 @@ Misc:
  - Qt: Disable Replace ROM option when no game loaded
  - Qt: Defer texture updates until frame is drawn (fixes mgba.io/i/1590)
  - Qt: Set icon for Discord Rich Presence
+ - Qt: Show a warning when save file can't be opened
 
 0.8.1: (2020-02-16)
 Emulation fixes:

src/gba/gba.c

@@ -432,7 +432,7 @@ bool GBALoadROM(struct GBA* gba, struct VFile* vf) {
 
 bool GBALoadSave(struct GBA* gba, struct VFile* sav) {
 	GBASavedataInit(&gba->memory.savedata, sav);
-	return true;
+	return sav;
 }
 
 void GBAYankROM(struct GBA* gba) {

src/platform/qt/CoreManager.cpp

@@ -109,7 +109,9 @@ CoreController* CoreManager::loadGame(VFile* vf, const QString& path, const QStr
 	}
 	bytes = info.dir().canonicalPath().toUtf8();
 	mDirectorySetAttachBase(&core->dirs, VDirOpen(bytes.constData()));
-	mCoreAutoloadSave(core);
+	if (!mCoreAutoloadSave(core)) {
+		LOG(QT, ERROR) << tr("Failed to open save file. Is the save directory writable?");
+	}
 	mCoreAutoloadCheats(core);
 
 	CoreController* cc = new CoreController(core);